Heat transfer block for cross flow heat exchanger

ABSTRACT

A heat transfer element for cross flow heat exchanger consists of ceramic corrugated and planar plates. A plurality of the heat transfer elements are stacked up in such a manner that the direction of corrugation in adjacent elements intersects at right angles to form a heat transfer block for cross flow heat exchanger. Concave portions of corrugation, which confront soot-blowing flow for removing soot deposited onto the heat transfer surfaces of heat transfer block, are filled with ceramic solids. Also concave portions of corrugation corresponding to the corners, which abut the packings attached when the heat transfer block is installed on a casing, are filled with ceramic solids.

BACKGROUND OF THE INVENTION

No. 1 Field of the Invention

The invention relates to a structure of a corrugated ceramic heattransfer block for a cross flow heat exchanger.

No. 2 Description of the Prior Art

Conventionally cross flow heat exchangers utilizing corrugated ceramicheat transfer blocks have been used, wherein the heat transfer blockutilized therein comprises heat transfer elements 10 each of which ismade of a corrugated plate of ceramics 11 and a planar plate of ceramics12 abutting each other, for example as shown in FIG. 4. As shown in FIG.5, a plurality of heat transfer elements 10 are stacked in multi-layersso that the direction of corrugation of corrugated plate 11 in anyelement alternately intersects at a right angle that in an adjacentelement, thereby forming a heat transfer block 20. Two kinds of fluidsat different temperatures flow through the heat transfer block 20 in twodirections shown by arrows A and B to exchange heat between each other.

FIG. 6 shows an example of a cross flow heat exchanger 30 which isconstructed of a plurality of heat transfer blocks which are assembledand tightened after considering the flow rates and allowable pressurelosses of fluids flowing therethrough. In this example, for instance,hot exhaust gas flows perpendicularly through the heat exchanger 30 inthe direction of arrows E, E', while cold air flows hoizontally, asshown by arrows C₁, C₂, C₃ and C₄, through the heat exchanger 30, heatbeing exchanged therebetween.

When heat exchange is conducted between exhaust gas E and combustion airC using this cross flow heat exchanger, a portion of the exhaust gas issuccessively cooled to below its dew-point as a result of heatexchanger, wherein soot in the exhaust gas E is deposited on the heattransfer surface. Since soot accumulated in the course of operationlowers the amount of heat transferred, soot blowing is conducted fromeither the inlet or outlet of exhaust gas E, or from both the inlet andoutlet of exhaust gas, to remove the deposited soot. Cold, warm or hotwater, water vapor, etc. may be suitably selected as a soot blowingfluid J injected from a soot blowing pipe 21, as shown in FIG. 7, andsoot removal is effected either by a separation action due to thetemperature difference between the soot blowing fluid J and thesoot/heat transfer surface, or by a separation action caused by animpacting force by the pressurized soot blowing fluid J which isinjected from small holes and impinged upon the soot, the separationeffect being generally thought to depend on the kind of fluid in theformer separation action, and on the pressure and density of the fluidin the latter action.

Referring to FIG. 6, when the heat transfer blocks 20 are installed ontoa casing 22, a heat transfer block holder 23 is used on each corner ofthe heat transfer block 20, and a packing 23a is interposed between theheat transfer block 20 and the heat transfer block holder 23.

The corrugated plate 11 and the planar plate 12 of the heat transferelement 10 shown in FIG. 4 are made of ceramic paper having a thicknessof about 1 mm. If a soot blowing impact of 0.5 to 0.7 g/cm² isrepeatedly applied by injecting soot blowing fluid J as shown in FIG. 7for soot removal, repeating this impact about 400 times may causethroughholes 11C to develop in the top end of the corrugated plate 11,air for combustion being leaked through the holes 11C, thereby renderingheat exchange impossible and impairing the function as a heat exchanger.

On the other hand, referring to FIG. 6, since only the end 20a ofceramic paper sheet contacts the packing 23a of the heat transfer block20, a tightening force is concentrated therein so that the end of theceramic sheet is broken or corrugation collapses, thereby impairingsealing performance. If soft packing made of bundles of glass wool,ceramic paper or the like is used, the packing 23a comes to envelopembrace the end 20a of the heat transfer block 20 of corrugatedceramics, thereby making the contacting area larger and easing theconcentration of tightening force. However, at the same time, exhaustgas and air for combustion pass through the interior of the packing,consequently impairing sealing capability.

BRIEF SUMMARY OF THE INVENTION

The invention seeks to provide a holding structure for a corrugatedceramic heat transfer block for a cross flow heat exchanger, in whichthe corrugated plates are not damaged by the impact of repeated sootblowing. The invention also seeks to provide a holding structure ofceramic heat transfer blocks, in which a tightening force on thecontacting portion of packing of heat transfer block is dissipated tohave better abutment of packing of heat transfer block.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective of an embodiment of the invention,

FIG. 2 is a perspective of another embodiment of the invention,

FIG. 3 is a partially cut away perspective of the embodiment in FIG. 2,

FIG. 4 is a perspective of a corrugated ceramic heat transfer element,

FIG. 5 is a perspective of a prior art heat transfer block,

FIG. 6 is a front elevation of a cross flow heat exchanger, and

FIG. 7 is a perspective illustrating the soot blowing operation on aprior art heat transfer block.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides, in one embodiment, a corrugated ceramic heattransfer block for cross flow heat exchanger in which a plurality ofheat transfer elements each made of a ceramic corrugated plate and aplanar plate are laid in multi-layers in such a manner that thedirection of corrugation in adjacent elements intersects at rightangles, characterized in that ceramic solids fill the concave portionsof corrugation of the heat transfer block, said portions confronting theflow of soot blowing for removing soot which is deposited on the heattransfer surfaces of the heat transfer block. The invention provides, inanother embodiment, a corrugated ceramic heat transfer block for a crossflow heat exchanger in which a plurality of heat transfer elements eachmade of a ceramic corrugated plate and a planar plate are laid inmulti-layers in such a manner that the direction of corrugation inadjacent elements intersects at right angles, characterized in thatceramic solids fill the concave portion of corrugation at a cornerabutting a packing which is attached when the heat transfer block isinstalled on a casing.

According to the invention, since ceramic solids fill the concaveportions of the heat transfer block, corrugated ceramic paper in theheat transfer element is reinforced, thereby protecting ceramic paperfrom the impact of soot blowing, and since ceramic solids are filled inthe corners of the heat transfer block which a packing abuts, atightening force is dissipated when the heat transfer block is installedon a casing, thereby preventing damage to the heat transfer block.

The following performance characteristics are required for ceramicsolids: first, waterproofness, acid-resistance, heat-resistance, andimpact-resistance to soot blowing and thermal shock-resistance, andsecond, adhesiveness to heat transfer block when filled in small spacesand anti-shrinkage upon heating.

In the invention, the materials for ceramic solids are not definitelyspecified as long as they satisfy the performance characteristicsrequired above, but preferably are mixtures of, for example, bindingmaterials, aggregates, reinforcing fibers and viscosity increasingsubstances.

Binding materials are used for the binding of other materials andadhesion thereof to the walls of structures and preferably are silicatebase binders such as silica gel, ethyl silicate and alkali silicate, andalumina sol, aluminum phosphate and similar materials.

Aggregates to be added for soot-blowing resistance, sealing, and otherproperties can be nonorganic powder commonly used such as calciumcarbonate and clay, but preferably are siliceous powder such as silicastone or amorphous silica, C-glass flakes, mica, titanium oxide,zirconia powder or the like, particularly where acid-resistance isrequired.

Reinforcing fibers to be used for thermal shrinkage resistance andthermal shock resistance, can be C-glass fibers, potassium titanatefibers and walastonite, but preferably are C-glass fibers, silica glassfibers, anti-alkaline glassy fibers particularly where acid-resistanceis required.

Viscosity-increasing substances to be added for preventing separationbetween binding material and aggregate and preventing flowing thereofafter filling, are preferably methyl cellulose, carboxymethyl cellulose,polyethylene oxide, sodium alginate and other organics, or bentonite,clay and other inorganics.

Embodiments

The invention will be described hereunder by way of embodiments withreference to the accompanying drawings.

FIG. 1 is a perspective of an embodiment of the invention. Since aceramic corrugated plate 11 and a planar plate 12 of a heat transferelement 10 are similar to those described in reference to FIG. 4, andsince the arrangement of the heat transfer elements in a heat transferblock is similar to that explained in reference to FIG. 5, furtherdescriptions thereof are omitted herein. In the embodiment of theinvention, as shown in FIG. 1, the cavity between the corrugated plate11 and the planar plate 12 at the top of the heat transfer element 10 isfilled with ceramic solids 13. The ceramic solids 13 are filled andfired during fabrication of corrugated ceramic heat transfer element 10in this case. The construction protects the corrugated plate 11 from theimpact of soot arising from soot blowing. Because of this arrangement,the corrugated plates 11 subject to impact did not show any damage evenafter the application of an impacting force of 0.5 to 0.7 g/cm² as manyas two thousand (2000) times. Consequently, stronger soot blowing at ahigher fluid supply pressure was made possible. It is better if theportions to be filled with ceramic solids are of gentle convex shapelike a barrel roof or equilateral triangular shape of low height, andthe solids overshoot the end of the element,

FIGS. 2 and 3 are perspectives of another embodiment of the invention.Since the construction of heat transfer block 20, heat transfer elements10, corrugated plates 11 and planar plates 12 in this embodiment aresimilar to those explained in reference to FIGS. 1 and 5, furtherdetails are omitted herein. A heat transfer block holder 23 as explainedin reference to FIG. 6 is installed at each corner of a heat transferblock 20 with a packing 23a interposed therebetween, and a plurality ofheat transfer blocks 20 are installed on a casing in the manner shown inFIG. 6. In the embodiment of the invention, ceramic solids 14 fill thespace between the corrugated plate 11 and the planar plate 12 in eachheat transfer element 10, that is, in the area where the heat transferblock 20 contacts the packing 23a. In this case, ceramic solids 14 arefilled and fired during fabrication of the heat transfer element 10.Because of this construction, concentration of tightening force onto theend portion of ceramic paper sheet is eliminated, thereby preventingbreakage of the end of ceramic paper sheet under that tightening force.

Further, the packing 23a used herein, in order to cover the roughsurface of filled ceramic solids 14, is preferably foamed fluorinerubber sheet or the like having individual pores with a porosity of 60to 70%, and being tightened to 1.5 kgf/cm².

Next, further specific embodiments of heat transfer blocks of theinvention will be described hereunder. A paper sheet for treatment of120 g/m² in weight and 1 mm in thickness was made, through a commonprocess, from zirconium-containing glass fiber (commonly known asalkali-resistant glass or ARG fiber) and a polyvinyl-alcoholic resinbase binder, and coated with silica powder of the rate of 300 g/m². Thispaper sheet was subjected to a common corrugating process, laminated andbonded together with the direction of corrugation (direction of fluidpassage) interchanged by 90°, thereafter impregnated with hardenersolution consisting of binder (colloidal silica) and aggregate (silicapowder, C-glass flakes), dried to harden and fired, this process beingrepeated three times to form a cross flow ceramic heat transfer block of300 mm cubed (300×300×300 mm).

This block had a wall thickness of 1.1 mm, flute height of 9 mm, pitchof 15 mm and density of 400 kg/m².

Next, the concave portions (non-flow passages) of correspondingcorrugation on four faces of the heat transfer block were filled withceramic solids consisting of a binder (colloidal silica), aggregate(silica powder, white carbon) and viscosity-increasing material (methylcellulose) to form gentle convexes like a barrel roof, dried to hardenand fired.

A number (N) of the blocks thus fabricated were installed on a casingwith packing applied to each corner of each block, the packing beingfoamed fluoric rubber sheet of density 0.4 kg/cm³ with a width of 20 mmand thickness of 5 mm. The blocks were tightened from the exterior ofcasing to apply face pressure of 1 kgf/cm² to the packings.

The results of soot blowing tests and leakage tests with this heattransfer block were appreciably better than that of the prior art. Theheat transfer block can also be made as follows:

(a) Zirconia-containing glass fiber can be replaced by C-glass fiber.

(b) The block of the embodiment can be further treated with resin ofcopolymer of tetrafluoroethylene-hexafluoropropylene (FEP).

According to the invention, ceramic solids were filled in the portionswhere impact or tightening force is applied in a corrugated ceramic heattransfer block for cross flow heat exchanger, thereby preventing thecorrugated heat transfer block from soot-blowing damage during sootblowing and preventing breakage of the ends of ceramic paper sheet ofheat transfer block.

As a number of wide variety of different embodiments of this inventionmay be made without departing from the spirit and scope thereof, it isto be understood that this invention is not limited to the specificembodiments thereof except as defined in the appended claims.

What is claimed is:
 1. A corrugated ceramic heat transfer block for alinear cross flow heat exchanger, in which a plurality of heat transferelements each composed of a ceramic corrugated plate member and aceramic flat plate member is stacked in such a manner that the directionof corrugation in adjacent elements intersects at right angles,characterized in that concave portions of said corrugation of said heattransfer block, which confront a blowing fluid stream for removing sootdeposited onto the heat transfer surfaces of said heat transfer block,are filled with ceramic solids, said concave portions being formedbetween said ceramic corrugated plate member and said ceramic flat platemember and extending at right angle to the soot-removing fluid streamflow direction, said ceramic solids being water-proof, acid-resistant,heat-resistant, resistant to impacts by said fluid stream, resistant tothermal shocks, adhesive to said heat transfer block when filled insmall spaces and resistant to shrinkage upon heating.
 2. A corrugatedceramic heat transfer block for a linear cross flow heat exchanger, inwhich a plurality of heat transfer elements each composed of a ceramiccorrugated plate member and a ceramic flat plate member is stacked insuch a manner that the direction of corrugation in adjacent elementsintersects at right angles, characterized in that said transfer block isfitted with block corner holders having packings fitted at and abuttingthe corners of said transfer block and with spaces formed between saidceramic corrugated plate member and said ceramic flat plate member, saidspaces being filled with ceramic solids that are water-proof,acid-resistant, heat-resistant, resistant to impacts by fluid-impingingstreams, resistant to thermal shocks, adhesive to said heat transferblock when filled in small places and resistant to shrinkage uponheating.